Smartphone case attachment



FIG. 1 is a front perspective view of a smartphone case attachment showing the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a left side view thereof.

The broken lines shown in the drawings depict portions of a smartphone that forms no part of the claimed design. 

CLAIM The ornamental design for a smartphone case attachment, as shown and described. 